1826.] Magnetism of Metals, S^c. arising from their Rotation. 189 



of the silk-thread however still embarrassed us a good deal. ' 

 But though this undoubtedly caused individual results to differ 

 more from the mean than we had expected, it is not sufficient to 

 accounf for a singular anomaly observed not only in the mean 

 results of a great number of trials, but in all individual cases ; 

 viz. that by this mode of observation, zinc was invariably found 

 to stand above copper in the scale of magnetic action, whereas 

 in the determination by the statical method, where the deviation 

 of the compass was observed, the former metal was as invariably 

 found to be placed below the latter, the other metals retaining 

 their order. 



Comparing the means obtained by the apparatus just described 

 of all the hnes in the table constructed of the results for copper, 

 zinc, tin, lead, and of the six first for copper and antimony, the 

 proportional intensity of magnetic action for each respectively 

 will be 



Zinc Ml 



Copper 1-00 



Tin 0-51 



Lead 0-25 



Antimony 0*01 



The smallness of the number for antimony is here also very 

 remarkable. That for bismuth deduced by this means would be 

 still more minute, so small indeed that the torsion of the thread 

 would not allow of its magnitude being fairly determined, the 

 suspended system merely performing extensive oscillations in 

 very long times. 



This method however requires us to operate on very consider- 

 able quantities of the substances under examination, a great 

 disadvantage, as it cannot be applied to the scarcer metals, and 

 does not admit of the use of the common ones in a state of rigo- 

 rous purity. A method at once more simple and expeditious, 

 and allowing of our acting on small quantities of matter, is to 

 suspend portions of the different bodies we would try, similar in 

 form and exactly equal in size, over the revolving magnet, and 

 noting either, dynamically the times of successive revolutions, 

 or, statically the point of equilibrium between the rotatory force 

 and the torsion of the string. This method we pursued in a 

 very interesting part of the inquiry, viz. in investigating (after 

 M. Arago) the effect of a solution of continuity, partial or total, 

 in the mass acted on. 



A disc of lead of two inches in diameter and one-tenth thick, 

 was suspended in a small thin wooden tray at a given distance 

 from the horse-shoe magnet, revolving with the usual velocity, 

 at first entire, and then successively cut with a chisel in radii 

 nearly up to the centre, as represented in the following page. 



